You can also test your phones services and hardware from this menu (main display, camera, LED/illumination, Flash LED, keyboard, earphone, speaker, microphone, radio and vibrator tests)

IMEI Number: *#06#

Lock status: <- * * <-

Shortcut to last dialed numbers: 0#

Shortcut to sim numbers: On main menu type a number and press #

If you change the language from default to any other language, then it may be difficult to switch to default language. The shortcut is very simple. Just press < 0000 > . < stands for left arrow button or joystick and > stands for right arrow button or joystick.